Method of reducing the surface leakage on a III-V semiconductor

ABSTRACT

The surface leakage on a III-V semiconductor is reduced by selectively  grng a mixed oxide on the surface of the semiconductor to passivate the semiconductor and reduce the surface leakage.

GOVERNMENT INTEREST

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

FIELD OF INVENTION

This invention relates in general to a method of reducing the surfaceleakage on a III-V semiconductor and in particular to such a methodwhere the III-V semiconductor is a gallium arsenide field effecttransistor FET.

BACKGROUND OF THE INVENTION

Gate leakage and gate to drain breakdown impose several constraints onthe operation of GaAs FET's. In particular, maximum power gain of highfrequency power transistors is limited by these quantities. The majorityof techniques for extending these limits have involved designmodifications of the FET such as locating the FET gate as far from thedrain as is possible while maintaining good high frequencycharacteristics.

SUMMARY OF THE INVENTION

The general object of this invention is to provide a method of reducingthe surface leakage on a III-V semiconductor. A more particular objectof the invention is to provide such a method that will reduce the gateleakage and increase the gate to drain breakdown voltage of GaAs FET's.A still further object of the invention is to provide such a method inwhich there will be no design constraints placed on the FET. Anotherobject of the invention is to provide such a method that is simple toimplement.

It has now been found that the aforementioned objects can be attained byselectively growing an oxide on the semiconductor surface thatpassivates the semiconductor surface and reduces the surface leakage.

In the instance when GaAs is the semiconductor, Ga₂ O₃ is selectivelygrown on the GaAs surface. GaAs can be oxidized by various oxidantsforming a mixed gallium-arsenic oxide. This oxide has very poorelectrical properties. Our desirable method forms the mixed oxide byphoto oxidation in water. In pH neutral water, the arsenic oxideselectively dissolves leaving a gallium oxide. Auger and RBS analysisshows the oxide to be Ga₂ O₃. This oxide passivates the GaAs surface andreduces the surface leakage. The amount of oxide required is only enoughto give good coverage of the surface. Hence, there is very littleetching of the GaAs during oxidation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The GaAs FET to be treated is placed in a container of deionized water.The immersed FET is illuminated with lamp light. The FET is removed whensufficient oxide has grown to effect the desired improvement of gateleakage and breakdown voltage, typically about 15 minutes. For a fixedvoltage, there is an order of magnitude reduction in gate leakage.

The aforesaid method of reducing gate leakage and increasing gate todrain breakdown voltage utilizes a post-fabrication surface treatment incontrast to imposing design constraints on the FET.

There are no design constraints on the FET according to the method ofthe invention. Moreover, the method is exceedingly simple to implementin that a light source and deionized water are the only equipmentneeded. Then too, the device to be treated needs no prior preparation.Also, the method is quick, typically requiring less than 30 minutes tocomplete.

The method of the invention may be used whenever it is desired to reducesurface leakage on any GaAs semiconductor device. The most immediateapplication is to GaAs microwave FET's for both commercial and militaryuse.

We wish it to be understood that we do not desire to be limited to theexact details of construction shown and described for obviousmodifications will occur to a person skilled in the art.

What is claimed is:
 1. Method of reducing the surface leakage on a III-Vsemiconductor comprising selectively growing a mixed oxide on thesurface of the semiconductor to passivate the semiconductor and reducethe surface leakage.
 2. Method according to claim 1 wherein the III-Vsemiconductor is a GaAs semiconductor.
 3. Method of reducing the gateleakage and increasing the breakdown voltage of a GaAs field effecttransistor (FET) comprising forming a mixed oxide by photo oxidation inwater to passivate the surface of the GaAs and reduce the surfaceleakage.
 4. Method according to claim 3 wherein the water is a pHneutral water in which arsenic oxide selectively dissolves leaving agallium oxide Ga₂ O₃ that passivates the GaAs surface and reduces thesurface leakage.
 5. Method of reducing the gate leakage and increasingthe breakdown voltage of a GaAs FET comprising immersing the FET in acontainer of deionized water and illuminating with a lamp and thenremoving the FET when sufficient oxide had grown to effect the desiredimprovement of gate leakage and breakdown voltage.
 6. Method accordingto claim 5 wherein the method requires less than 30 minutes to complete.